Nickel plating



Oct. 6, 1953 c, CASE 2,654,705

NICKEL PLATING Filed NOV" 24, 1950 FIGZ INVENTOR. Bernard 6? Case ATTORNEYS Patented Oct. 6, 1953 NICKEL PLATIN G Bernard 0. Case, Howell Mich., assignor to Banson-Van Winkle-Munm'ng Company, Detroit, Mich., a corporation of New Jersey Application November 24, 1950, Serial N 0. 197,317

9 Claims.

This invention relates to the electrodeposition of nickel, commonly called plating, and particularly to an improved nickel anode, a method of preparing the anodes and a method of plating adapted to effect the more satisfactory deposition of nickel in plating operations.

This application is a continuation in part of my application Serial No. 749,731 filed May 22, 1947, now abandoned.

In the customary plating operation, nickel anodes are suspended in a solution of nickel salts called the electrolyte. Upon the application of a suitable electric current, nickel is deposited at the cathode (the work-piece to be plated) and is dissolved simultaneously from the anode to replenish the nickel content of the electrolyte. The anodes commonly used are of rolled or cast nickel which dissolve uniformly as the operation proceeds. Such anodes are relatively costly as compared with commercial electrolytic nickel.

Electrolytic nickel is the product of the Well known process for the electrolytic refining of nickel. It comes from the refinery usually in large sheets about a quarter of an inch thick, and substantially square. The nickel is of high purity (about 99.95% including cobalt) and is in this respect entirely suitable for use in an electrolytic plating operation. Nickel produced by electrolytic refining can be distinguished from east nickel by the fact that it shows a columnar structure with the column axis perpendicular to the face of the cathode; and the term electrolytic nickel is used herein and in the appended claims to refer to such nickel.

Unfortunately, electrolytic nickel is not adaptable (except as hereinafter explained) for use as the anode of a plating operation. Instead of dissolving uniformly over the surface as rolled or cast anodes do, electrolytic nickel begins to dissolve under usual plating conditions by showing a deeply pitted structure. As the application of the current continues, electrolytic nickel may separate into layers having a lacework structure. The inside of the anode becomes very porous. Flakes of the metal drop off and fall into the bottom of the anode bag. Occasionally a large piece of solid nickel drops because the metal surrounding it has been eaten away.

Another reason why it ha not been found practicable to operate plating baths with electrolytic nickel anodes is the fact that when a number of such anodes are suspended from a common bar, as they are in commercial practice,

individual anodes show marked variations in behavior. It is not uncommon to find difierences in potential between individual anodes on the same bar as high as 100 to 200 millivolts. Since the anode bar acts as a common source of our:

able.

conform to the conditions necessary for opera-- tion of the patented procedure.

The primary object of the present invention: is to provide an anode of electrolytic nickel mod-- ified so that it may be used generally in nickel plating electrolytes to produce the desired results.

Another object of the invention is the provision of a method of treating electrolytic nickel to modify its characteristics so that it may be used successfully in the deposition of nickel in connection with the usual electrolytes.

A further object of the invention is the provision of a method of electrodepositing nickel in a more economical and commercially advantageous manner.

Other objects and advantages of the invention will be apparent as it is better understood by ref erence to the following specifications and the accompanying drawing, in which Fig. 1 is a diagrammatic illustration of a plating operation;

Fig. 2 is a phot-omicrograph showing the columnar structure in a piece of commercial electrolytic nickel; and

Fig. 3 is a similar photomicrograph showing an equi-axed grain structure with coarse but fairly uniform grains developed in the same piece of nickel by the procedure hereinafter described.

I have discovered that electrolytic nickel which normally has the columnar metallographic structure as shown in Fig. 2 may be modified by suitable heat treatment to provide throughout the metal an equi-axed grain structure with coarse, uniform grains as shown in Fig. 3, and that such modified electrolytic nickel, when used as the anode in a plating operation, dissolves smoothlyusing electrolytic. nickel anodes by modifying the electrolyte so as. to provide conditions favorable for smooth cor-- rosion of the electrolytic nickel. This is accom-- plished by correlating the chloride content and"v value of the electrolyte within well definecL limits. The results obtained following the opti mum conditions laid down by Pinner are excel-.- lent. However, the modifications required in the electrolyte considerably restrict performance at; the cathode and influence the resulting nickeli deposit in a manner which is not always desir Moreover, the procedure does not permit; the use of standard electrolytes which do not:

and uniformly in the electrolyte, essentially as a cast nickel anode does. Thus the difficulties heretofore experienced in attempting to use electrolytic nickel as the anode in a plating operation are avoided.. The electrolyte used may. be. any of those Tcom'm'only employed in electrolytic plating operations, and the other normal conditions of such operations may be unchanged. Hence it becomes possible to employ commercial electrolytic nickel without the necessity for remelting; casting or rolling. The heattreatment-isa releg tively simple operation whichwcanj be..-carried;out under the conditions hereinafter described.

The sheets of electrolytic nickel as received. from the refinery always have the characteristic columnar structure shown in Fig. 2. The grain size, however, may vary according to the conditions under which the nickel has: been deposited. When Qheat'treated so, as to. produce recrystallizae tion or, the nickel, the columnar Structure changesjtojah equieaxed structure. I have found that when recrystallization. is. carried out at lowertemperaturfe's, 'the'gria'in size of the recrysalli'zed'n'lckelma'y vary considerably, depending not only. on the temperature and the time of heatingfbut al'sfoyon the conditions under which the 'electrolyticfnickel was deposited. on the other hand, if recrystallization is carried .out at a high enough temperaturethe time or heating and the 'conditions'ojf deposition no longerfseein to, be significant factor's coarse, grains of fairly uniform size areprodu'ced irrespective of'the time of 'heating and o'f the previous history of the nickel undergoing this heat treatment.

Themgl i n pb lt of pure nickel is. approximately 2645 degrees Fahrenheit. I prefer to carry out theheat treatment 'ofelectrolytic nickel 'atatemperature notfar below the melting point, preferably between 2200 andv 2500 degrees Fahrenheit and in-any case above 2100 degrees. There is no reason why the temperature should not go above 2500- degrees-except the risk of melting the nickelifthe meltingpoint is ap; pr'gachedtoo closely, Within this temperature range, namely above 2100 degrees and below the melting point, essentially the same results are obtained irrespective of the time of heating: for example, by induction, heating for seconds or by soaking aGlobar furnace for 30 minutes. Likewise, annealing for an hour or 'more at a lower temperature before pushing up to the higher temper'aturehas been found to have .no appreciableeirect;

The structure obtained by recrystallizing electrolytic nickel in this manner is always 'of the equi-axed type. The range of grain size and the average grain-size produced by annealing at varying temper'atures a-re" shown in the following table. These grainsize measurements were made by projecting theiinage-of suitably polished specimens on the ground glass plate o'f a'metallurg'ical microscope-at a magnification of 100 diameters and comparing'with standard non ferrousmetal grain size charts of the American Society for Testing Materials.

2100 degrees.

size would be approximately 0.090 millimeter or *la-rger.

The average grain size in the above table cor responds closely to the size of grain found with greatest frequency.

As stated above, the preferred temperature for heat treating electrolytic nickelirr accordance with my invention is froin2-20'0 degrees to about 2500 degrees Fahrenheit and in no case under The corresponding average grain Whentherehas been an interruption in current. while the electrolytic nickel is being de- -p.osited,.:theeffect is to show an interruption line which can be seen under the microscope andsometimeseven'with the naked eye. Wherever: a;discontinuity of this kind occurs, the grain size immediately adjacent thereto tends to remain smaller after heat treatment than the main body'of the electrolytic nickel. But the use of annealing temperatures in the range specified above insures that, even in these areas, grain growth is adequate. Hence current inter ruption lines are not a significant factor in the overall performance or suchh'eat treatedelectr'olytic nickel when used as 'an anode for nickel plating.

The treatment described'brin'gs aboutia cor= responding "change in respect to the hardness. Electrolytic nickel after this'heattreatment be comes'dead softfi" The heating maybe carried outjby, any suitablemeans, such, for example, as induction heating or heatingin a muiile'furnaeeora salt bath. It is desirable to avoid oxidizing the nickel; which may be'done by using a neutral or'reducing atmosph'ere." The particular type of furnace or fuel employed form's nopart orthe invention, since many furnaces and fuels suitable for'the purpose are readily available.

Individual pieces of electrolytic nickel" heat treated in accordance with this invention behave uniformly when-suspended from a common'a'node bar, a's-is the-practicein commercial plating; The difieren'ce in potential among such 'individual anodes -is-usually-under a millivolt. The? dissolve smoothly and-uniformly many of the common electrolytes used for nickel plating without leaving an objectionable amount of insoluble The-proportions as above stated may bewari'ed; and addition agents may beincluded. Since the foregoing example is merely illustrative, it is "to beunderstoodthat theinvention is not restricted to any particular electrolyte. The modified electrolytic nickel :described' herein has been round-to be operative as the anode in electrolytes including nickel salts of various kinds and in various proportions. Thus, the anode may be used in an electrolyte containing only nickel chloride and free from sulphate.

The operating conditions such as pH and temperature of the electrolyte, the anode current density and the cathode current density may also be varied over the usual range common in commercial practice. As a typical example, the following conditions are suitable:

Temperature 130 F.

Cathode current density 40 amp. per square foot. Anode current density 40 amp. per square foot.

None of these conditions is critical in respect to the uniform solution of the electrolytic nickel anode modified in accordance with the present invention.

The invention as described aifords a marked improvement in the technic of nickel plating, in as much as entirely satisfactory results are obtainable with a variety of electrolytes and the usual operating conditions. The expense incident to the preparation of nickel anodes as heretofore practiced is avoided, since the heat treatment of electrolytic nickel can be conducted at relatively slight expense and the modified electrolytic nickel produced by that treatment dissolves uniformly in the electrolyte under normal plating conditions and permits the disposition of satisfactory nickel coatings.

The term "cathode sheet as used in the appended claims is to be understood as including tubes, bars or rods deposited as a cathode in the electrolytic refining of nickel and modified in accordance with the present invention.

The above detailed description has been given by way of explanation and illustration only, and not by way of limitation. Various changes may be made in the procedure as described without departing from the invention or sacrificing the advantages thereof.

I claim:

1. An anode for use in the electrodeposition of nickel consisting of a cathode sheet of electrolytic nickel having the normal columnar grain structure modified by heating to a temperature of from about 2200 degrees F. to slightly less than the melting point of nickel to an equi-axed grain structure with an average grain size not less than about 0.090 millimeter throughout the body thereof.

2. An anode for use in the electrodedeposition of nickel consisting of a cathode sheet of electrolytic nickel having the normal columnar grain structure modified by heating to a temperature of from about 2200 degrees F. to slightly less than the melting point of nickel to an equi-axed grain structure with an average grain size not less than about 0.090 millimeter throughout the body thereof, the grain size varying from 0.035 to over 0.200 millimeter.

3. An anode for use in the electrodeposition of nickel consisting of a cathode sheet of electrolytic nickel having the normal columnar grain structure modified by heating to a temperature of from about 2200 degrees F. to slightly less than the melting point of nickel to an equi-axed grain structure with a grain size exceeding 0.035 millimeter throughout the body thereof, the grain size averaging approximately 0.090 millimeter.

4. The method of preparing an anode for use in the electrodeposition of nickel which consists of subjecting a cathode sheet of electrolytic nickel to a temperature of from about 2200 degrees F. to slightly less than the melting point of nickel to modify the normal columnar metallographic structure of the metal to an equi-axed grain structure with an average grain size not less than about 0.090 millimeter.

5. The method of preparing an anode for use in the electrodeposition of nickel which consists of subjecting a cathode sheet of electrolytic nickel to a temperature of from about 2200 degrees F. to slightly less than the melting point of nickel to modify the normal columnar metallographic structure of the metal to an equi-axed grain structure with a grain size not less than about 0.035 millimeter and ranging to over 0.200 millimeter and averaging not less than about 0.090 millimeter.

6. The method of preparing an anode for use in the electrodeposition of nickel which consists of subjecting a cathode sheet of electrolytic nickel to a temperature of from about 2200 degrees F. to 2500 degrees F. to modify the normal columnar metallographic structure of the metal to an equi-axed grain structure with a grain size averaging approximately 0.090 millimeter.

7. The method of electrodepositing nickel which comprises suspending the work-piece to be plated in an electrolyte containing a nickel salt in solution with an anode consisting of a cathode sheet of electrolytic nickel in which the norma1 columnar metallographic grain structure has been modified by heating to a temperature of from about 2200 degrees F. to slightly less than the melting point of nickel to an equi-axed grain structure with a grain size not less than about 0.035 millimeter and ranging to over 0200 millimeter and averaging not less than about 0.090 millimeter, and connecting a source of current to the work-piece and anode.

8. The method of electrodepositing nickel which comprises suspending the work-piece to be plated in an electrolyte containing a nickel salt in solution with an anode consisting of a cathode sheet of electrolytic nickel in which the normal columnar metallographic grain structure has been modified by heating to a temperature of from about 2200 degrees F. to slightly less than the melting point of nickel to an equi-axed grain structure with a grain size exceeding about 0.035 millimeter and averaging approximately 0.090 millimeter, and connecting a source of current to the work-piece and anode.

9. The method of electrodepositing nickel which comprises suspending the work-piece to be plated in an electrolyte containing a nickel salt in solution with an anode consisting of a cathode sheet of electrolytic nickel in which the normal columnar metallographic grain structure has been modified by heating to a temperature of from about 2200 degrees F. to slightly less than the melting point of nickel to an equi-axed grain structure with an average grain size not less than about 0.090 millimeter, and connecting a source of current to the work-piece and anode.

BERNARD C. CASE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,433,618 Hogaboom Oct. 31, 1922 2,297,766 Hull Oct. 6, 1942 2,453,757 Renzoni Nov. 16, 1948 

1. AN ANODE FOR USE IN THE ELECTRODEPOSITION OF NICKEL CONSISTING OF A CATHODE SHEET OF ELECTROLYTIC NICKEL HAVING THE NORMAL COLUMNAR GRAIN STRUCTURE MODIFIED BY HEATING TO A TEMPERATURE OF FROM ABOUT 2200 DEGREES F. TO SLIGHTLY LESS THAN THE MELTING POINT OF NICKEL TO AN EQUI-AXED GRAIN STRUCTURE WITH AN AVERAGE GRAIN SIZE NOT LESS THAN ABOUT 0.090 MILLIMETER THROUGHOUT THE BODY THEREOF. 